1. Field of the Invention
The present invention relates to lasers and particularly to a diode-pumped, Tm-doped, CW, solid state laser that is continuously tunable between about 2.20 microns and about 2.46 microns.
2. Description of the Related Art
Interest in the development of tunable solid state lasers has increased significantly in recent years. For example, development of room temperature solid state lasers in the two-micron spectral range has received much attention recently because of potential applications in medicine and optical communications. An exemplary, room temperature, tunable solid state laser that operates in the two-micron range is taught in U.S. Pat. No. 4,969,150 (Esterowitz et al.). U.S. Pat. No. 4,969,150 is directed to an end-pumped, Tm.sup.3+ ion-doped, solid state laser for producing a CW laser emission continuously tunable over the approximate spectral range of 1.86 to 2.14 microns.
The Tm.sup.3+ ion-doped in a solid state medium or host exhibits a high multiplicity of Stark level splittings due to the interaction of its partially shielded 4f electrons with the local crystal field The combination of closely spaced Tm.sup.3+ energy levels, coupled with significant phonon broadening in the lattice, allows for the broad tunability of this rare earth ion in a variety of hosts. The .sup.3 F.sub.4 -.sup.3 H.sub.6 Tm.sup.3+ transition, for example, has been continuously tuned from 1.85 microns to 2.15 microns in YAG (yttrium aluminum garnet) and YSGG (yttrium scandium gallium garnet).
Laser action at 2.3 microns based on the .sup.3 H.sub.4 -.sup.3 H.sub.5 Tm.sup.3+ transition has been demonstrated in several garnet and fluoride hosts. The development of efficient, diode-pumped, tunable laser sources operating in this wavelength region of from about 2.20 microns to about 2.46 microns is of interest for chemical detection and remote sensing applications. Unfortunately, previous laser operation of the 2.3 micron laser has been either at a single wavelength or at several wavelengths that were not continuously tunable. A major reason for this is that laser performance of the Tm.sup.3+, .sup.3 H.sub.4 -.sup.3 H.sub.5, 2.3 micron transition is affected by multiphonon decay and Tm.sup.3+ ion-pair cross-relaxation. Each of these mechanisms nonradiatively depletes the .sup.3 H.sub.4 laser level, resulting in reduced fluorescence lifetimes and correspondingly high CW lasing thresholds.
Thus, at the present time, there is a need for a tunable solid state laser that can produce a CW laser emission that is continuously tunable over the approximate spectral range of from 2.20 microns to 2.46 microns for various chemical detection and remote sensing applications.